Needle bar drives for zigzag sewing machines



April 12, 1960 R. E. JOHNSON NEEDLE BAR DRIVES FOR ZIGZAG SEIINGMACHINES Filed June 24, 1958 Ralph E Johnson ATTORNE United StatesPatent NEEDLE BAR DRIVES FOR ZIGZAG SEWING MACHINES Ralph E. Johnson,Mountainside, N. l., assignor to The Singer Manufacturing Company,Ehzabeth, N.J., a corporation of New Jersey Application June 24, 1958,Serial No. 744,153

3 Claims. (Cl. 112-421) pensating for the variations at loop seizure ina zigzag sewing machine in the position of the eye of the needlerelatively to the path of motion of the loop seizing beak in thedilferent positions of the needle.

Having in mind the above and other objects that will be evident from anunderstanding of this disclosure, the invention comprises the devices,combinations and arrangements of parts as illustrated in the presentlypreferred embodiment of the invention which is hereinafter set forth insuch detail as to enable those skilled in the art readily to understandthe function, operation, construction and advantages of it when read inconjunction with the accompanying drawings in which:

Fig. 1 is a fragmentary vertical sectional view longitudinally of asewing machine embodying the present invention;

Fig. 2 is a schematic view illustrating the various vertical positionsof the needle in the mechanism of Fig. 1 as it is moved laterally duringzigzag sewing.

Figs. 3 and 4 are fragmentary sectional views taken substantially on theline 3-3 of Fig. l and showing the needle bar drive in differentpositions.

The present invention is herein disclosed as embodied in the sewingmachine forming the subject matter of my pending application Serial No.471,766, filed November 29, 1954, now Patent No. 2,862,468. The machineincludes a frame having a bed 1 and a bracket arm 2 terminating in ahead 3 that overhangs the bed 1. Mounted in the bed 1 is a vertical axisrotary hook 4 having a loop seizing beak 5. The hook 4 cooperates with athread carrying needle 6 in the formation of lock stitches.

The needle 6 is secured to the lower end of a needle bar 7 that ismounted in the head 3 for endwise reciprocation and for lateralvibration. the lower portion of the needle bar 7 is mounted for endwisesliding in a ball bearing 8 that is seated in a two-part socket element9 arranged in a bore in the bottom of the head 3 and held therein by anexternally threaded sleeve 10. At its upper end, the needle bar 7 ismounted for endwise sliding in a ball bearing 11 that is seated in asocket in a pivoted gate member 12 and held therein by an externallythreaded sleeve 13. Oscillation is imparted to the gate member 12 by apitman 14 that is driven by a needle bar vibrating mechanism. Uponoscillation of gate member 12, through the connection at the ballbearing 11, the needle bar 7 is moved laterally about the axis definedby the ball bearing 8.

Endwise reciprocation is imparted to the needle bar 7 by the main shaft15 of the machine, which shaft is journaled longitudinally of thebracket arm 2. Mounted upon the end of the main shaft 15 is a crank 16having a crank pin 17 upon which one end of a needle bar Moreparticularly,

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i drive link 18 is pivotally mounted. At its opposite end,

the link 18 is provided with a hub 19 having a bore 20 in which a stud21 is freely mounted for turning and for endwise sliding. The stud 21 isintegral with a drive member 22 mounted on the needle bar 7 for pivotalmovement about an axis diametrically of the needle bar and for unitarymovement endwise of the needle bar, the drive member 22 being in theform of a yoke that includes oppositely extending arms that embrace theneedle bar 7 and are pivotally secured thereto by a diametricallyarranged pivot pin. 7

During stitch formation, the needle bar is reciprocated endwise topenetrate the work and from the point. of maximum penetration, it risesto throw a loop on the underside of the work that is then entered by theloop seizing beak. There is an optimum delay, which is approximatelytwenty degrees of arm shaft rotation, in the illustrated machine,between the time the needle reaches the point of maximum penetration andthe time that the beak enters the loop which is calculated to produce aneedle thread loop that is sufliciently large to insure loop seizure andto position the eye of the needle in a specific relationship to the loopseizing beak for the proper presentation of the loop to the loop seizingbeak. In a straight-away sewing machine, timing of the needle relativelyto the loop taker does not present a problem. However, in a zigzagsewing machine, the optimum timing relation is effected by the lateralvibrations of the needle. Thus, when the needle is moved in onedirection, loop seizure is retarded by the amount of time required forthe loop taker to travel from the previous position of loop seizure tothe new position of loop seizure. Since the needle bar continues to riseduring the time that the loop taker is traveling to the new position,the optimum timing relationship between them is destroyed, or morespecifically, the eye of the needle is too high. Conversely, when theneedle is moved in the other direction, loop seizure is advanced withthe result that the eye of the needle is too low.

Heretofore, in zigzag sewing machines, the needle was timed relativelyto the loop taker to obtain the optimum relationship in the zero bightposition or in other words, in the position in the center of the zigzagpattern. Thus, the effects of the variations in the time of loop seizurewere minimized. The resulting variations from the optimum tintingrelationship however, did increase the number of skipped stitches thatresulted from failure of the loop taker to seize the loop and alsoincreased the incidence of thread breakage'resulting from fouling of theloop.

In accordance with the present invention, there is provided a simple andeffective means for compensating for the variations in the timing of theneedle relatively to the loop taker during zigzag sewing. This meanscomprises angling the axis of the needle bar driving stud 21 relativelyto the axis of the needle bar 7. More particularly, the stud 21 isarranged at an acute angle which, in the illustrated machine, isapproximately eight degrees to a line normal to the axis of the needlebar rather than normal to the axisof the needle bar or in other words,to the axis of the main shaft 15 rather than parallel to the axis of themain shaft, so that as the stud 21 moves endwise in the bore 20 it willeffect an endwise displacement of the needle bar 7. The effect of thiscompensation is illustrated schematically in Fig. 2 in which the eye ofthe needle 6 is represented at 23. In the position at the center of thezigzag pattern, which is illustrated in full lines, the eye 23 of theneedle is in its optimum relation relatively to the beak 5 of the looptaker at loop seizure. When the needle bar 7 is pivoted about the ball 8to shift the needle 6 laterally to the right to the position illustratedin broken lines, the stud 21 moves endwise out of the bore 20, thus ineffect raising the needle bar 7 and the needle 6 so that the eye 23 iscloser to the path of the beak 5. With the needle shifted to the right,loop seizure will occur sooner than in the full line position since thebeak will arrive at the loop seizing position sooner. Normally, withoutmeans for compensating for this effect in the timing relation, the eye23 would be too low relatively to the path of the beak 5 since it hasnot had sufficient time to allow for rising to the designed optimumposition. In accordance with the present invention, the lateral movementof the needle bar 7, by the proper selection of the angle of inclinationof the stud 21, will raise the needle bar 7 by an amount equal to thedistance that the eye 23 would be below the designed optimum positionthat results from the earlier loop seizure. The net effect of thiscompensation is that the eye 23 of the needle is in the designed optimumposition at loop seizure. In Fig. 2 there is illustrated only the resultobtained by swinging the needle about the ball 8. Since in the rightposition loop seizure will occur approximately ten degrees earlier, theeye 23 of the needle 6 will actually be at loop seizure in the positionillustrated at 23a, which is exactly its designed optimum positionrelatively to the beak 5.

Conversely, when the needle is swung about the pivot defined by the ball8 to the left hand position, which is illustrated in dotted lines inFig. 2, the movement of the stud 21 into the bore 20 lowers the needlebar 7. In this position, the time of loop seizure occurs later so thatthe eye 23 of the needle 6 would normally be too high by an amountdefined by the continued needle bar rise as the beak 5 moves theadditional distance to the new position of loop seizure. The additionalrise of the needle bar coupled with the lowering of the needle bar as itis swung laterally that results from the fact that the stud 21 is angleddownwardly, has the net effect of positioning the eye of the needle atthe position 23b at loop seizure, which again is the designed optimumrelation relatively to the beak 5. I

Another important advantage derived from the present construction isthat the needle bar 7 is turned slightly about its longitudinal axis bythe action of the angled stud 21, which action breaks the frictionalresistance between the needle and the work and thereby reduces flagging,which is the tendency of the work to follow the needle. As illustrated'in Figs. 3 and 4, as the crank pin 17 is rotated from the one side ofthe needle bar 7 to the other side, the angle of approach of the link 18is shifted with the result that in horizontal plan as shown in Figs. 3and 4 the angle of the stud 19 relatively to the axis A of the mainshaft shifted between a position in which the axis B of the stud 21 ison opposite sides of the axis A of the main shaft. The maximum anglesbetween the axes A and B of course occurs when the crank pin 17 isninety degrees in front of and ninety degrees beyond its top dead centerposition. The greatest amount of the turning motion occurs around thetop and bottom dead center positions with the rate of the turning motionapproaching-zero and then reversing in a sinusoidal manner at the ninetydegree positions. Thus, about the bottom dead center position of thecrank pin 17 which is when the needle reaches its point of maximumpenetration and begins to rise, there is a maximum amount of turningmotion which acts to break the frictional engagement between the needleand the work and reduces the tendency of the work to follow the needleas it is withdrawn.

Numerous alterations of the structure herein disclosed will suggestthemselves to those skilled in the art. However, it is to be understoodthat the present disclosure relates to a preferred embodiment of myinvention which is for purposes of illustration only and not to beconstrued as a limitation of the invention. All such modifications whichdo not depart from the spirit of the invention are intended to beincluded within the scope of the appended claims.

Having thus described the nature of my invention, what I claim hereinis:

1. In a sewing machine having a frame, a loop taker journaled in saidframe, a needle bar mounted in said frame for endwise reciprocation andfor turning about its longitudinal axis, a needle carried by said needlebar and adapted to cooperate with said loop taker in the formation ofstitches, means for imparting endwise reciprocation to said needle bar,and means for imparting a cycle of turning to said needle bar upon eachreciprocation thereof and including a turning movement at the time thatthe needle bar begins to rise from the point of maximum penetration anda reverse turning movement at the time that the needle bar begins todescend from the point of maximum rise.

2. In asewing machine having a frame including a head, a needle barmounted in said head for endwise reciprocation and for turning about itslongitudinal axis, a drive member mounted on said needle bar for pivotalmovement about an axis diametrically of said needle bar and for unitarymotion with said needle bar in a direction longitudinally of andangularly about the axis of said needle bar, a drive stud extendinglaterally from said drive member, means for imparting endwisereciprocation and turning to said needle bar comprising a crank mountedin said frame for rotation about an axis substantially normal to theaxis of said needle bar and having a crank pin on an axis parallel tothe axis of said crank, a link connected at one end to said crank pinand at its other end having a bore on an axis inclined at an acute angleto a line parallel to the axis of said crank, said drive stud beingmounted in said bore for turning and.

for endwise sliding.

3. In a zigzag sewing machine having a frame including a head, a needlebar mounted in said head for endwise reciprocation, for lateralvibration and for turning about its longitudinal axis, a drive membermounted on said needle bar for pivotal movement about an axisdiametrically of said needle bar and perpendicular to the plane definedby the lateral vibration of the needle bar and for unitary motion withsaid needle bar in a direction longitudinally of and angularly about theaxis of said needle bar, a drive stud extending laterally from saiddrive member, means for imparting lateral vibration to said needle barand means for imparting endwise reciprocation and turning to said needlebar comprising a crank mounted in said frame for rotation about an axissubstantially normal to the axis of said needle bar and having a crankpin on an axis parallel to the axis of said crank, a link connected atone end to said crank pin and at its other end having a bore on an axisinclined at an acute angle to a line parallel to the axis of said crank,said drive stud being mounted in said bore for turning and for endwisesliding movement.

References Cited in the file of this patent UNITED STATES PATENTS1,386,323 De Voe Aug. 2, 1921 1,474,269 Lautenschlager Nov. 13, 19232,662,495 Parry Dec. 15, 1953

